Respiratory tract infections (RTIs) are infectious diseases involving the lower or upper respiratory tract.

An infection of this type usually is further classified as an upper respiratory tract infection (URI or URTI) or a lower respiratory tract infection (LRI or LRTI).

Lower respiratory infections, such as pneumonia, tend to be far more severe than upper respiratory infections, such as the common cold.

The upper respiratory tract is considered the airway above the glottis or vocal cords; sometimes, it is taken as the tract above the cricoid cartilage.

This part of the tract includes the nose, sinuses, pharynx, and larynx.

Typical infections of the upper respiratory tract include tonsillitis, pharyngitis, laryngitis, sinusitis, otitis media, certain influenza types, and the common cold.

Symptoms of URIs can include cough, sore throat, runny nose, nasal congestion, headache, low-grade fever, facial pressure, and sneezing.

Lower respiratory tract infection consists of the trachea, bronchial tubes, bronchioles, and the lungs.

Lower respiratory tract infections (LRIs) are generally more severe than upper respiratory infections.

LRIs are the leading cause of death among all infectious diseases.

The two most common LRIs are bronchitis and pneumonia.

Influenza affects both the upper and lower respiratory tracts.

More dangerous strains such as the highly pernicious H5N1 tend to bind to receptors deep in the lungs.

The response to infection involves immune activation and the local release of both proinflammatory and anti-inflammatory mediators.

The release of such mediators the alveolar capillary barrier leads to interstitial and alveolar edema and then the development of pulmonary fibrosis.

The host responded to pulmonary infection is activation of the hypothalamus – pituitary adrenal access by inflammatory cytokines.

Treatment:

Antibiotic use is not recommended for common bacterial infections as the immune system will resolve such infections.

Antibiotic do not effectively treat a viral infections

Despite the superior filtration capability of N95 filtering facepiece respirators in vitro, insufficient clinical evidence exists to determine whether standard surgical masks and N95 filtering facepiece respirators are equivalent to preventing respiratory infections in healthcare workers.

The combination of topical and systematic antibiotics taken prophylactically can prevent infection and improve adults’ overall mortality in the ICU for adult patients receiving mechanical ventilation for at least 48 hours, and topical antibiotic prophylaxis probably reduces respiratory infections but not mortality.

The combination of treatments contributes in the systemic component of the observed reduction of mortality.

There is no sufficient evidence to recommend that antibiotics be used to prevent complications from an RTI of unknown cause in children under the age of 5 years old.

High-quality clinical research in the form of randomized controlled trials assessed the effectiveness of Vitamin D,[26] another review of poorer quality RCTs addressed the effectiveness of immunostimulants for preventing respiratory tract infections.

Exercise may reduce severity of symptoms but had no impact on number of episodes or number of symptom days per episode.

Viruses that cause RTI are more transmissible at very high or low relative humidity; ideal humidity for indoor spaces is between 40 and 60%.

Controlling relative humidity in this range can help lessen the risk of aerosol transmission.

Respiratory infections often have strong seasonal patterns: more affected during the winter.

Winter peaks in respiratory infections are due to environmental conditions and changes in human behaviors.

Viruses that cause respiratory infections are affected by environmental conditions like relative humidity and temperature: temperate climate winters have lower relative humidity, which is known to increase the transmission of influenza.

Viruses that cause respiratory infections in humans have seasonal variation in prevalence: Influenza, Human orthopneumovirus (RSV), and human coronaviruses are more prevalent in the winter.

Rhinoviruses, which cause the common cold, occur mostly in the spring and fall, and human parainfluenza viruses have variable peaks depending on the specific strain.

Enteroviruses, tend to peak in the summer.

Current management of severe primary infections includes antimicrobial and respiratory support, with supplemental oxygen therapy and mechanical ventilation.

Corticosteroids can mitigate the inflammatory response.

Corticosteroids inhibits the expression of pro-inflammatory genes, decreasing T cell proliferation and cytokine production, impairing migration of immune cells through effect on adhesion molecules and chemokine signaling and activating kinase pathways.

Treatment with low-dose cortical steroids is associated with decreased mortality for patients with severe COVID-19 infection, severe community acquired, bacterial pneumonia, moderate severe Pneumocystis pneumonia, and may benefit in critically ill patients with respiratory infections who have septic shock, acute respiratory distress syndrome or both.